Is honesty a bad thing? Plato says it is

He came up with setting out arguments in the syllogistic form which was a big step in being able to assess the validity of arguments. But you're right in saying he didn't invent rationality.

I doubt Plato was a communist in the modern sense. He certainly would not have understood the concept of taking populations from one country and throwing them into another which is what modern communism seems to advocate.

Here he also seems to voicing the vegetarian simplicity position which Percy Shelley repeated in the 19th century. It also suggests not only the conflict created by tribalism but technological complexity which I think goes hand in had these days:

Plato Republic book 2

Socrates: Will not tutors be also in request, and nurses wet and dry, tirewomen and
barbers, as well as confectioners and cooks; and swineherds, too, who
were not needed and therefore had no place in the former edition of our
State, but are needed now? They must not be forgotten: and there will
be animals of many other kinds, if people eat them.

Glaucon: Certainly.

S: And living in this way we shall have much greater need of physicians
than before?

G: Much greater.

S: And the country which was enough to support the original inhabitants
will be too small now, and not enough?

G: Quite true.

S: Then a slice of our neighbours' land will be wanted by us for pasture
and tillage, and they will want a slice of ours, if, like ourselves,
they exceed the limit of necessity, and give themselves up to the
unlimited accumulation of wealth?

G: That, Socrates, will be inevitable.

S: And so we shall go to war, Glaucon. Shall we not?

G: Most certainly.